Various types of electrophysiology devices are used for ablating tissue. Typically, such devices include a conductive tip or blade which serves as one electrode in an electrical circuit which is completed via a grounding electrode coupled to the patient. With sufficiently high levels of electrical energy between the two electrodes, heat is generated which is sufficient to denature proteins within the tissue and cause cell death.
It is well known that by controlling the energy level, the amount of heat generated and degree of tissue damage can also be controlled. High levels of voltage can cut and remove tissue (i.e. electrosurgery), while lower levels will simply create sufficient heat to cause cell damage, but leave the structure intact and block electrical pathways within the tissue. Irrigation of the electrodes with saline or other conductive fluid can decrease the interface impedance, cool the tissue, and allow for a greater lesion depth. It is also know that a bipolar system (where the grounding electrode is in close proximity to the conductive tip) can create narrower and deeper lesions. At the limit, the grounding electrode is in the same dimension as the conductive tip, and both electrodes are used to create the lesion.
A bipolar ablation design may be created by integrating the electrode into the jaws of a hemostat (or forceps) like device. Mounting two electrodes onto the jaws of a forceps results in a tool that can clamp and ablate the tissue between the jaws.
A wide variety of surgical procedures involve ablation of selected tissue. One such procedure is the Maze procedure, which is a surgical operation for patients with atrial fibrillation that is resistant to medical treatment. In the conventional version of this procedure, incisions are created in the right and left atria to produce an orderly passage of the electrical impulse from the sino-atrial node (SA node) to the atrial-ventricular node (AV node). Blind passageways are also created to suppress reentry cycles. Ablation of cardiac conduction pathways in the region of tissue where electrical signals are malfunctioning is now being used to replace surgical incisions in the Maze procedure. Ablation is also used therapeutically with other organ tissues, such as the lungs, liver, prostate, and uterus. Ablation may also be used in treatment of disorders, such as tumors, cancers, or undesirable growths. There are various types of ablation devices that are in use and in development that are intended for use in the Maze procedure.
Sometimes ablation is necessary only at discrete positions along the tissue. At other times, ablation is desired along a line, called linear ablation. This is the case for atrial fibrillation, where the aim is to reduce the total mass of contiguous (electrically connected) atrial tissue below a threshold believed to be critical for sustaining multiple reentrant wavelets. Linear lesions are created between electrically non-conductive anatomic landmarks to reduce the contiguous atrial mass. One way of accomplishing linear ablation is to use a pair of bipolar electrosurgical forceps having jaws with an elongated electrode or series of electrodes used to apply energy to tissue for ablation purposes. One embodiment of this approach is described in U.S. patent Publication No. 2003/0171745, published Sep. 11, 2003, and titled “Ablation System and Method of Use,” which is incorporated herein by reference in its entirety.
In conjunction with the use of electrosurgical ablation devices, various control mechanisms have been developed to control delivery of ablation energy to achieve the desired result of ablation (killing of cells at the ablation site while leaving the basic structure of the organ to be ablated intact). Additionally, there has been substantial work done toward assuring that the ablation procedure is complete, i.e. that the ablation extends through the thickness of the tissue to be ablated, before terminating application of ablation energy. This desired result is referred to as “transmural” ablation. Non-transmural lesions may be capable of propagating a depolarization wave form, or action potential and may not be effective in treating an arrhythmia. One embodiment of a system for assessing the transmurality of an ablation lesion is described in U.S. patent Publication No. 2003/0195384, published Oct. 16, 2003, and titled “System and Method for Assessing Transmurality of Ablation Lesions,” which is incorporated herein by reference in its entirety.
One challenge associated with ablation procedures relates to determining the proper energy to apply to the tissue and duration of application of that energy in order to achieve the desired transmurality. One approach is to estimate tissue thickness and then to consult a look-up table to determine an experimentally determined energy and duration associated with that thickness. However, such an approach requires an accurate assessment of tissue thickness, which may also present a challenge. Further, depending on the type of device used to apply ablation energy to the tissue, further variables may be introduced. For example, when using a hemostat type device, the pressure between the jaws is a function of the force applied to the handles any may vary depending on the person holding the device. Such variability impacts the most effective treatment time and energy.
The design challenge with any ablation device, and in particular with a hemostat type device, is to create a lesion having consistent quality, in particular a continuous linear lesion when engaging in the Maze procedure. Further, it is desirable to create a lesion that is not too wide and that may be created in the least amount of time. Further, a challenge in the creation of such a device is to reduce the variability based upon the user such that a device may be used by various users with consistent results.
Accordingly, there is a need for an ablation device that is configured to permit a consistent application of appropriate force at the tissue site when in use. Further, there is a need for a device configured to permit real time assessment of lesion transmurality while in use. Further still, there is a need for an ablation device having the ability to aid in the determination of ablation parameters, such as degree of applied force, time of treatment, and treatment energy.
It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed herein extend to those embodiments that fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.